Diy Home-car Subwoofer

[Tasmaniak]

the 80 watt amp from Jaycar is NOT I repeat NOT an automotive amplifier.

You will hear the 80 watts just fine. But, be aware that underpowering a speaker is harmful to amplifier and speaker.

 

[Astranomical]

You could use a computer power supp to provide the 12V power.

Good idea, preferably an AT power supply. (that is, one from a 486 or early Pentium), as then you don't need to have a motherboard hooked up for it to turn on.